let map = new Map([
    [1,'one'],
    [2,'two'],
    [3,'three'],
]);

let arr=[...map.keys()]
console.log(arr);

const [f,...rest] = [1,2,3,4,5]
console.log(f);


let a = {
'0':'a',
'1':'b',
'2':'c',
length:3    
};

let arr1 = Array.from(a)

console.log(arr1);

let ar = Array.from('hello');
console.log(ar);


let b = Array.from({length:4})
console.log(b);

let al = Array.from([1,3,6,7],x => x*x);
console.log(al);

console.log(Array.from({length:3},() => 'jack'));
//需要一个lerater接口

console.log(Array(3));